a three-level lc-switching-based voltage boost npc...

2876 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 64, NO. 4, APRIL 2017

A Three-Level LC-Switching-BasedVoltage Boost NPC Inverter

Manoranjan Sahoo, Student Member, IEEE, and Sivakumar Keerthipati, Member, IEEE

Abstract—A single-stage high-voltage gain boost inverteris getting popularity in applications like solar photovoltaic,fuel cell, uninterruptible power system (UPS) systems, etc.Recently, single-stage voltage boost multilevel Z-sourceinverter (ZSI) and quasi-Z-source inverter (QZSI) have beenproposed for dc–ac power conversion with improved powerquality. Multilevel ZSI uses more number of high-power pas-sive components in the intermediate network, which in-crease the system size and weight. Also, its input currentis discontinuous in nature which is not desirable in someof the applications like fuel cell, UPS systems, hybrid elec-tric vehicle, etc. In this paper, a continuous current inputthree-level LC-switching-based voltage boost neutral-point-clamped inverter is proposed, which uses comparativelyless number of high-power passive components at the sametime retains all the advantages of multilevel QZSI/ZSI. It isable to boost the input dc voltage and give required three-level ac output voltage in a single stage. Steady-state anal-ysis of the proposed inverter is discussed to formulate therelationship between the input dc voltage and three-levelac output voltage. A unipolar pulse width modulation tech-nique devised for the proposed inverter to eliminate firstcenter band harmonics is also presented. The proposedconverter has been verified by simulation in MATLABSimulink as well as performing experiment with the helpof a laboratory prototype.

Index Terms—Boost inverter, pulse width modulation(PWM), shoot through, three-level inverter, Z-source inverter(ZSI).

NOMENCLATURE

Ton Shoot-through period.

Ts Switching time period.

D Shoot-through duty ratio (ratio of Ton to Ts).

Vdc DC voltage fed before the inverter leg fromdc side.

Ii Average dc input current.

Vg Input dc voltage.

Vm Peak ac phase voltage at output.

M Modulation index.

VC 1 , VC 2 Voltages across the capacitors C1 , C2 ,respectively.

Manuscript received April 22, 2016; revised June 29, 2016, August11, 2016, and September 12, 2016; accepted October 11, 2016. Date ofpublication December 6, 2016; date of current version March 8, 2017.

The authors are with the Department of Electrical Engineering, IndianInstitute of Technology Hyderabad, Hyderabad 502285, India (e-mail:[email protected]; [email protected]).

Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIE.2016.2636120

IC 1 , IC 2 Currents through the capacitors C1 , C2 ,respectively.

VL1 , VL2 Voltages across the inductors L1 , L2 , respectively.

IL1 , IL2 Currents through the inductors L1 , L2 ,respectively.

I. INTRODUCTION

CURRENTLY, the multilevel voltage-source inverter (VSI)is used in a wide range of applications like photovoltaic

(PV) system, uninterruptible power supply (UPS), fuel cell,wind power, hybrid electric vehicle (HEV), etc., [1]–[4]. Themultilevel VSI provides advantages like better power quality,smaller output ac filter requirements, lower voltage stress acrossthe inverter switches, etc. However, the conventional multilevelVSI behaves like buck converter [5], i.e., peak ac output voltageis less than the input dc-link voltage. In applications like PVsystem, fuel cell, UPS, etc., the required ac output voltage levelis achieved by using either a dc–dc converter before the VSI ora transformer after the VSI [6], [7], but more number of powerconverter stages increases system control complexity and de-creases the system efficiency [8]. Similarly, an inclusion of linefrequency transformer increases the system size and weight [9].In multilevel VSI, shoot-through (i.e., switching all the switchesin the inverter leg) results dead short circuit of the source. Shootthrough is avoided by providing dead band between switchingcontrol signal fed to the complementary switches of inverter leg,which introduces distortion in the output ac voltage.

The Z-source inverter (ZSI) addresses the above issues andis able to boost the input dc voltage to achieve the requiredac voltage in a single stage [10]–[13]. Conventional three-levelZ-source neutral-point-clamped (NPC) inverters are exploredfor medium-power and low-power applications [14], [15]. Itprovides better power quality at the same time voltage stressacross switches and output filter requirements are less. This usestwo isolated dc sources which may require isolation transformerand additional rectifier circuits (in case isolated dc sources arenot readily available). It is primarily operated in three states,i.e., nonshoot-through state, zero state, and shoot-through state.In multilevel ZSI, shoot-through state is utilized along with pas-sive reactive element to boost the input dc voltage. It is similarto the zero state of multilevel VSI where no power is trans-ferred to the load. In nonshoot-through state, power is trans-ferred from dc source to ac load, which is similar to the activestate of the multilevel VSI. However, the use of more num-ber of high-power passive reactive elements in the intermediate

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SAHOO AND KEERTHIPATI: THREE-LEVEL LC-SWITCHING-BASED VOLTAGE BOOST NPC INVERTER 2877

Fig. 1. Circuit diagram of a three-level LC-switching voltage boost NPC inverter.

network as well as isolated dc power supply increases the sys-tem size, weight, and cost. In literature [16], [17], a single LCimpedance network-based three-level ZSI is discussed whichuses less number of high-power passive components (two ca-pacitors and two inductors) and single split-dc source, but inthis multilevel inverter, the voltage rating of the capacitor isnearly double than the conventional three-level Z-source NPCinverter. The source/input current of the three-level NPC ZSI isdiscontinuous in nature which may increase the stress on sourceand is not desirable in some of the application like fuel cell,ups system, HEV, etc., [18], [19]. Multilevel quasi-Z-sourceinverter (QZSI) is an improved derivative of a multilevel ZSI[20], where the source current is continuous in nature and volt-age stress across the inverter switches are comparatively less.Cascaded quasi-Z-source multilevel inverter uses two or moreisolated dc sources and more number of high-power passivereactive elements for better quality single-stage power conver-sion as discussed in [21]–[23]. Similarly, a three-level NPCQZSI is discussed in [24], where a quasi-Z-source network isincorporated with conventional NPC structure to give multileveloutput. However, the use of more number of high-power passivereactive elements and multiple isolated dc power supply in mul-tilevel QZSI [20]–[22] increases the system size, cost, as well asweight. In this paper, a three-level LC-switching-based voltageboost NPC inverter is proposed for boosting the input voltageand give required three-level ac output voltage in a single stage.It uses comparatively less number of passive reactive elements(only two inductors and two capacitors), two active switches,and four diodes in the intermediate network between dc sourceand inverter leg at the same time it provides all the advantagesof multilevel QZSI. As a result, system size and weight are re-duced. Though the cost of extra switches and diodes are notmuch less than the extra passive components (inductors and ca-pacitors) used in multilevel QZSI but can be used in low-poweror medium-power applications where size and weight are main

constraints. Rest of this paper is organized as follows. Opera-tion of the proposed converter with different operating modesand mathematical validation is presented in Section II. A pulsewidth modulation (PWM) technique is discussed in Section III,experimental and simulation results are discussed in Section IV,and the paper is ended with a conclusion in Section V.

II. THREE-LEVEL LC-SWITCHING-BASED VOLTAGE

BOOST NPC INVERTER

Fig. 1 shows the schematic diagram of a three-level LC-switching-based voltage boost NPC inverter, which is able toboost the input dc voltage source (“Vg”) and give requiredthree-level ac voltage unlike conventional NPC VSI. Here, theinput source can be either two equal dc sources or single splitdc source. This single split dc can be created by feeding a dcsource parallel to two series-connected capacitors, where theinterconnection point between these capacitors can be taken asneutral point [26]. The intermediate network between dc sourceand inverter leg is comprised of two inductors (L1 , L2), two ca-pacitors (C1 , C2), two active switches (S1 , S2), and four diodes(D1 , D2 , D3 , and D4). Whereas a conventional three-levelZ-source NPC inverter uses four inductors, four capacitors, andtwo diodes in the intermediate network between inverter legand input dc as discussed in the literature [14], [15]. In theseconventional Z-source NPC inverters, diodes are connected inseries with the input dc source to boost the voltage and the in-put current is discontinuous in nature. In [24], the NPC QZSIis discussed, where the input current is continuous in nature,but it uses equal values of four inductors, four capacitors, andtwo diodes in the intermediate network as discussed in SectionI. The proposed inverter, however, uses half of the number ofpassive components (two inductors and two capacitors) in theintermediate network by utilizing extra two switches (S1 andS2) and two diodes at the same time maintains all the advan-


TABLE ISWITCHING STATE AND SWITCHING COMBINATION OF AN LC-SWITCHING

BOOST NPC INVERTER (x = 1, 2, 3)

State of Operation ON Switches Voltage

Nonshoot-through state Sw x 1 , Sw x 2 +Vd c

Nonshoot-through state Sw x 3 , Sw x 4 −Vd c

Shoot-through state S1, S2, Sw x 1 , Sw x 2 , Sw x 3 , Sw x 4 0Zero state Sw x 2 , Sw x 3 0

Fig. 2. Equivalent circuit during nonshoot-through state operation ofan LC-switching boost NPC inverter.

tages of NPC QZSI. As a result, the proposed inverter can beuseful in the applications where size and weight are main con-straints. Traditional NPC three-level VSI is basically operated intwo states, i.e., active state (or nonshoot-through state) and zerostate to give three distinct voltage levels (i.e., +Vdc , 0, −Vdc).Whereas the proposed inverter uses additional one more state,i.e., shoot-through state to boost the input dc voltage and givethree distinct voltage levels (+Vdc , 0, −Vdc) in a single stage.The detailed switching pattern at each state is summarized in Ta-ble I. The possible modes of operation of the proposed inverterare discussed as below.

A. During Nonshoot-Through State (or Active State)

It is similar to the active state of conventional NPC VSIwhere power is transferred from dc source to ac load. In thisinterval of operation, the ac load attains either “+Vdc” or “−Vdc”voltage level across ac load with respect to neutral point “n.”The switches Swx1 and Swx2 (where x = 1, 2, 3) are switched“ON” and switch “S1” is switched “OFF” to achieve “+Vdc”across ac load with respect to neutral point “n,” which in turnforward biases the diodes “D1” and “D2 .” As a result, bothsource “Vg ” and inductor “L1” energize the capacitor “C1” aswell as supply power to the load, as shown in Fig. 2. Similarly,

Fig. 3. Equivalent circuit during zero-state operation of an LC-switchingboost NPC inverter.

the switches Swx3 and Swx4 are switched “ON” and switch “S2”is switched “OFF” to achieve “−Vdc” across ac load with respectto neutral point “n,” which in turn forward biases the diodes“D3” and “D4 .” As a result, both source “Vg ” and inductor“L2” energize the capacitor “C2” as well as supply power to theload, as shown in Fig. 2. Here, for easy understanding, the loadhas been represented by current source as for small duration theload current is assumed to be constant.

B. During Zero State

In this state, no power is transferred to ac load from dc sourcesimilar to the zero state of conventional NPC VSI. The switchesSwx2 and Swx3 are switched “ON” and switches “S1 ,” “S2 ,”“Swx1 ,” and “Swx4” are switched “OFF” to achieve “0” voltageacross load, which in turn forward biases the diodes “D1 ,” “D2 ,”“D3 ,” and “D4 .” As a result, upper source “Vg ” and inductor“L1” energize the capacitor ”C1” as well as lower source “Vg ”and inductor “L2” energize the capacitor “C2 ,” as shown inFig. 3.

C. During Shoot-Through State

During this mode of operation, the switches “S1” and “S2”and all the switches of one or more inverter legs are turned “ON,”which in turn reverse biases the diodes “D1 ,” “D2 ,” “D3 ,” and“D4 .” As a result, upper dc voltage source “Vg ” and capacitor“C1” energize the inductor “L1 .” At the same time, lower dcvoltage source “Vg ” and capacitor "C2” energize the inductor“L2 ,” as shown in Fig. 4. Shoot-though state is placed insidethe conventional zero state, without interfering the nonshoot-through state (i.e., active state). In nonshoot-through state andzero state ((1−D) Ts), the voltage across inductors “L1” and


Fig. 4. Equivalent circuit during shoot-through state operation of anLC-switching boost NPC inverter.

“L2” are found to be (from Figs. 2 and 3)

VL1 = Vg − VC 1 (1)

VL2 = Vg − VC 2 . (2)

Similarly, currents through the capacitors “C1” and “C2” arefound to be

iC 1 = iL1 − iac (3)

iC 2 = iL2 − iac . (4)

During shoot-through state (DTs), the voltages across induc-tors “L1” and “L2” are found to be (from Fig. 4)

VL1 = Vg + VC 1 (5)

VL2 = Vg + VC 2 . (6)

The currents through the capacitors “C1” and “C2” are foundto be

iC 1 = −iL1 (7)

iC 2 = −iL2 . (8)

Applying volt–second balance in steady-state equilibriumacross the inductors “L1” and “L2”, respectively, [21]

(Vg − VC 1) (1 − D) + (Vg + VC 1) D = 0 (9)

(Vg − VC 2) (1 − D) + (Vg + VC 2) D = 0. (10)

Solving (9) and (10), the voltage gains at capacitors “C1” and“C2” are found to be

VC 1 = VC 2 =Vg

(1 − 2D). (11)

Fig. 5. Relationship plot of voltage gain factor (G) versus shoot-throughduty ratio (D) versus modulation index (M).

Applying charge-second balance in steady-state equilibriumacross the capacitors “C1” and “C2”, respectively, [21]

(iL1 − iac) (1 − D) − DiL1 = 0 (12)

(iL2 − iac) (1 − D) − DiL2 = 0. (13)

Solving (12) and (13), the input current is found to be

Ii = IL1 = IL2 =(1 − D)iac

(1 − 2D). (14)

From the equivalent circuit (see Fig. 2), it can be observed thatthe dc voltage fed to the inverter leg “Vdc” during active state(i.e., nonshoot-through state) is equal to the capacitor voltages.

The peak output ac phase voltage is found to be

Vm = MVdc =MVg

(1 − 2D). (15)

The boost factor of the converter is found to be

B =1

(1 − 2D). (16)

The voltage gain factor (G) of the inverter can be expressedas

G =M

(1 − 2D). (17)

The relationship between voltage gain factor (G), shoot-through duty ratio (D), and modulation index (M) is presentedin a 3-D surface plot, as shown in Fig. 5. From this relation-ship plot as well as (15), it is observed that the LC-switchingboost NPC inverter can be operated as a buck–boost converterby choosing suitable values of M and D to get required outputac load voltage. From (11), it can be noticed that the convertercannot be operated with shoot-through duty ratio (D) more than0.5 similar to ZSI. For ensuring shoot-through state not to over-lap nonshoot-through state (or active state) in any switchingcycle, the shoot-through period can be taken maximum up to


zero state, i.e.,

M + D ≤ 1. (18)

Under continuous-conduction mode of operation, the induc-tors current ripple (ΔiL1 and ΔiL2) and capacitors voltage rip-ple (ΔVC 1 and ΔVC 2) of the inverter can be expressed as

ΔiL1 =Vg + VC 1

L1DTs (19)

ΔiL2 =Vg + VC 2

L2DTs (20)

ΔVC 1 =IL1

C1DTs (21)

ΔVC 2 =IL2

C2DTs. (22)

From the above relationships, it is observed that based onthe allowable inductor current ripple or input current ripple fordifferent applications, suitable values of inductors (L1 and L2)can be used. Similarly based on allowable dc-link voltage ripplefor different applications suitable values of capacitors (C1 andC2) can be used. By increasing switching frequency also valuesof these passive components can also be optimized further.

III. PWM CONTROL OF AN LC-SWITCHING BOOST

NPC INVERTER

The gate control signal for the inverter leg switches is gener-ated using a unipolar PWM technique in each phase for eliminat-ing first center band harmonics as well as to achieve three-levelpole voltages [25]. Here, for each phase, two modulating sinewaves of 180° phase displacement (Va(t) and –Va(t)) are com-pared with high-frequency triangular carrier signal (Vtri(t)), asshown in Fig. 6. For three phases, these modulating signals(Va(t) and –Va(t)) are phase displaced by 120° and comparedwith triangular carrier signal to generate gate control signal forthe inverter leg switches. The shoot-through gate signal is gen-erated by comparing two fixed reference signals (Vst and −Vst)with the carrier signal (Vtri(t)). The voltage gain factor (G)decides the amplitude of fixed signals (Vst and −Vst) as wellas modulating signals (Va(t) and −Va(t)). For ensuring shoot-through state not to impede active state (or nonshoot-throughstate), shoot-through state is placed within the zero state in eachswitching cycle, as shown in Fig. 6. To ensure voltage balanceacross the capacitors, a shoot-through offset is added by usingthe control logic presented in [28]. The shoot-through gate sig-nal is fed to the switches in the intermediate network (“S1” and“S2”). Whereas gate signal fed to the inverter leg switches arethe combination of shoot-through signal as well as signal gen-erated from the comparison of modulating signals and carriersignal.

IV. SIMULATION AND EXPERIMENTAL RESULTS

The proposed inverter has been analyzed and verified by per-forming simulation in MATLAB Simulink as well as experi-ment. The experimental validation has been done by developing

Fig. 6. PWM control of an LC-switching voltage boost NPC inverter.

TABLE IIPARAMETERS USED IN THE EXPERIMENT

Parameter Attributes

Input voltage (Vg ) 48 VInductor (L1 ) 6 mHInductor (L2 ) 6 mHCapacitor (C1 ) 2000 µFCapacitor (C2 ) 2000 µFAC output phase voltage (Vp h ) 110 V (rms), 50 HzCarrier frequency (fs ) 2.5 kHzModulating signal frequency (fm ) 50 HzLoad (Zl ) per phase 160 Ω

a laboratory prototype. The circuit parameters have been takenfor simulation and are shown in Table II. The LC-switchingboost NPC multilevel inverter has been simulated to achievephase voltage (Vph ) of 110 V (rams) from 48-V input dc supply(Vg ). Using (15) and (18), for the above desired phase voltage,shoot-through duty ratio (D) as well as modulation index (M)have been found to be 0.4091 and 0.5909, respectively. Car-rier frequency (fs) of 2.5 kHz has been used to generate PWMgate signal fed to the switches. Modulating signal frequency hasbeen taken same as the frequency of the required output ac volt-age. Performing simulation, the voltage developed across boththe capacitors “C1” and “C2” has been found to be the sameas theoretical values (using (11)), i.e., VC 1 = VC 2 ≈ 260 Vwith negligible ripple, as shown in Fig. 7(c) and (d). Similarly,the input current (iL ) for the load 160 Ω has been found to besame as estimated values (calculated using (14)), i.e., iL ≈ 6 A,as shown in Fig. 7(b). A three-level pole voltage (Van ) hasbeen observed with amplitude +260, 0, −260 V, as shown inFig. 8(d). Similarly, phase voltage (Vph ), phase current (Ipoh ),


Fig. 7. (a) Input dc voltage (Vg ) in volts versus time in seconds. (b) Inputcurrent (IL ) in amperes versus time in seconds. (c) Voltage developedacross capacitor C1 (Vc1 ) in volts versus time in seconds. (d) Voltagedeveloped across capacitor C2 (Vc2 ) in volts versus time in seconds ofan LC-switching voltage boost NPC inverter.

and line voltage (Vab ) have been observed to be same as theo-retical value as shown in Fig. 8(a)–(c), respectively. The totalharmonic distortion (THD) of the phase voltage for the aboveload condition has been found to be nearly 28.71%, as shown inFig. 9.

For experimental validation, a laboratory prototype has beendeveloped for 48-V dc input (Vg ) and 110 V (rms) output phasevoltage (Vph ), as shown in Fig. 10. A 220-W load has been con-nected to the inverter. Inductors and capacitors have been cho-sen same as taken in simulation. PWM signals have been gen-erated using field-programmable gate array (FPGA)-based pro-gramming in Xilinx Board (Spartan-6 XC6SLX9). TLP250 andSN5401 ICs have been used as gate driver circuit and buffer cir-cuit, respectively. To achieve the above required phase voltage,shoot-through duty ratio (D) and modulation index have beentaken same as simulation, i.e., 0.4091 and 0.5909, respectively.From Fig. 11(b), it can be noticed that the voltage across thecapacitors has been boosted to 253 V, which is nearly 5.5 timesthe input dc voltage (Vg = 48 V). At the same time, it is alsoobserved that the voltage across both the capacitors is balanced.The voltage developed across the two capacitors is same as thevoltage developed capacitors of NPC QZSI for the same ”D” and“M.” The voltage ripple of capacitors voltages can be controlledwith suitable value of capacitors (C1 and “C2"). Here, capacitorshave been designed for negligible voltage ripple (<0.01%). Theinput voltage and current waveforms are shown in Fig. 11(a). Itcan be noticed that the average input current is nine times theload current (i.e., rams current per phase). The input current of

Fig. 8. (a) Phase voltage (Vph ) in volts versus time in seconds.(b) Phase current (Ipoh ) in amperes versus time in seconds. (c) Line-line voltage (Vab ) in volts versus time in seconds. (d) Pole voltage (Van )in volts versus time in seconds at three-phase load of an LC-switchingvoltage boost NPC inverter.

Fig. 9. Harmonic spectrum of an LC-switching boost NPC inverterphase voltage (Vph ).

the multilevel ZSI is discontinuous, whereas it is continuous inthe proposed inverter and using (19), (20), its ripple content canbe controlled with the suitable value of inductors “L1”and “L2”.Here, inductors have been designed for 66% peak-to-peak cur-rent ripple. This ripple content of the inductor current has beenchosen to observe the performance of the proposed inverter inone of the extreme cases like allowing nearly maximum rip-ple current through the inductors at the same time maintainingnegligible voltage ripple across the capacitors. The performanceof the inverter will be better by taking lower inductor current


Fig. 10. Laboratory prototype of an LC-switching voltage boost NPCinverter.

Fig. 11. Experimental results of an LC-switching boost NPC inverter.(a) Input voltage (Vg ) and input current (IL ). (b) Boost voltage acrosscapacitors (VC 1 and VC 2 ).

ripple into consideration at the same time relaxing on capacitorvoltage ripple based on the allowable ripple content for differentapplications. The three-level pole voltage (Van ) (i.e., +253, 0,−253 V) has been observed, as shown in Fig. 12. The line-to-linevoltage has been found to be 1.73 times the pole voltage, i.e.,VA = 440 V, as shown in Fig. 12. Due to the associated noidealities, it can be realized that the voltage amplitudes of ex-perimental results are less than the theoretical values. The exper-imental phase voltage and phase current are as shown in Fig. 13.The peak value of the phase voltage (Vm ) has been observed tobe 156 V (i.e., 110-V rams) which is 3.25 times the input dcvoltage (Vg ). The THD of the phase voltage has been found to

Fig. 12. Experimental waveform of pole voltage (VAn ) and line-linevoltage (Vab ).

Fig. 13. Experimental results of phase voltage (Vph ) and phase current(Ipoh ).

Fig. 14. Efficiency versus load curve of an LC-switching boost NPCinverter.

be 29.71%. The efficiency of the LC-switching boost NPC in-verter has been found nearly equal to 89%, as shown in Fig. 14.Whereas the maximum efficiencies of NPC QZSI [24], cascaded[21], and the inverter presented in [27] have been found to benearly 91%, 85%, and 84.9%, respectively. The efficiency ofthe proposed inverter is little low because of additional switchesand diodes which introduces switching losses, but the use of


less number of passive elements in the inverter reduces systemvolume and weight.

V. CONCLUSION

In this paper, a three-level LC-Switching voltage boost NPCinverter was presented. The proposed inverter is able to boostthe input dc voltage and give required three-level ac output in asingle stage unlike conventional NPC VSI. It utilizes the shoot-through state for boosting up the voltage. In comparison to three-level conventional NPC ZSI and NPC QZSI, the LC-switchingboost inverter uses single split dc source as well as less numberof high-power passive reactive elements which results weightand size reduction. In addition to these advantages, the contin-uous input current of the proposed inverter makes it suitable forthe applications like fuel cells, UPS system, PV system, etc.The steady-state operation of the inverter is discussed and volt-age gain function is derived. PWM control strategy used for theswitching as well as restriction on modulation index and shoot-through duty ratio is also presented. The simulation has beencarried out using MATLAB Simulink along with experimentalanalysis has been done by developing laboratory prototype toverify the proposed inverter.

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Manoranjan Sahoo (S’16) received the B.Tech.degree in electrical and electronics engineeringfrom the Silicon Institute of Technology,Bhubaneswar, India, in 2011, and the M.Tech.degree in power electronics and power systemfrom the Indian Institute of Technology Hyder-abad, Hyderabad, India, in 2015, where he iscurrently working toward the Ph.D. degree inmultilevel boost inverters for renewable energyapplications.

His research interests include design of boostinverters, multilevel boost inverters, and microgrids.

Sivakumar Keerthipati (M’12) received theB.Tech. degree in electrical engineering fromSri Venkateswara University, Tirupati, India, in2004, the M.Tech. degree in power electron-ics and drives from the National Institute ofTechnology, Warangal, India, in 2006, and thePh.D. degree from the Center for Electronics De-sign and Technology, Indian Institute of Science,Bangalore, India, in 2010.

He is currently an Associate Professor in theDepartment of Electrical Engineering, Indian In-

stitute of Technology Hyderabad, Hyderabad, India. His research in-terests include multilevel inverters, open-end winding induction motordrives, pulse width modulation techniques, switched-mode power con-version, microgrids, and power quality and control.

a three-level lc-switching-based voltage boost npc...

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